1. Field of the Invention
This invention relates to a process for electrolytically coloring aluminum or any of its various alloys.
2. Prior Art
For electrolytic coloring of aluminum or aluminum alloy, there has been proposed and used a process wherein the basis metal is first anodized to form an oxide film thereon and then, with the pores in this oxide film unsealed, electrolyzed in an electrolytic solution containing a metallic salt such as a nickel salt by use of alternating or direct current. The basis metal is colored by electrodeposition of the metal or metal oxide in the pores of the oxide film thereon. This process has gained widespread acceptance in the industry partly because of the high weather resistance of the colored coatings produced.
The colored coating produced by such a prior art process, however, is generally poor in uniformity, so that particularly in the case of an irregularly shaped workpiece, its protuberant and recessed portions tend to be tinted in noticeably different shades. Another disadvantage is that a further decrease in the uniformity of coloring takes place if the basis metal is allowed to stand too long after the anodic treatment or if the basis metal is rinsed too long, particularly in liquid having a low pH value, after the anodic treatment.